package jingdong;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

/**
 * Created by lxy_920912 on 07/04/2017.
 */
public class Main2 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        double[] percent = new double[num];
        for(int i = 0;i < num;i++){
            percent[i] = ((double)scanner.nextInt())/100;
        }
        int MinNum = (int)Math.ceil((double)(num * 0.6));
        int[] combin = new int[num-MinNum+1];
        for(int i = MinNum;i <= num;i++){
            combin[i-MinNum] = combin(num,i);
        }
        List<Double> subset = new ArrayList<>();
        List<Double> result = new ArrayList<>();
        result.add(0.00);
        for(int i= MinNum;i <= num;i++){
            subSet(percent,0,i,subset,result,combin,MinNum,0);
        }

        System.out.println(result.get(0));

    }
    public static int combin(int n,int m){

        int x = 1;
        int y = 1;
        for(int i = 0;i < m;i++){
            x = x *(n-i);
            y = y * (i+1);
        }
        int result = x/y;
        return result;
    }
    public static void subSet(double[] precent,int start,int n,List<Double> subset,List<Double> result,int[] combin,int MinNum,int count){
        if(start >= precent.length){
            return ;
        }
        if(count >= n){
            double thisResult  = 1;
            for(int i = 0;i < subset.size();i++){
                thisResult = thisResult * subset.get(i);
            }
            if(start < precent.length){
                for(int i = start;i < precent.length;i++){
                    thisResult = thisResult*(1-precent[i]);
                }
            }
            thisResult = result.get(0)+thisResult;
            result.remove(0);
            result.add(thisResult);
            return;
        }

        subset.add(precent[start]);
        subSet(precent,start+1,n,subset,result,combin,MinNum,count+1);
        int len = subset.size();
        subset.remove(len-1);
        subset.add(1-precent[start]);
        subSet(precent,start+1,n,subset,result,combin,MinNum,count);
        subset.remove(len-1);
    }

}

//4
//50 50 50 50
//